[Solved] Arrangements and arrears

Hi, Newbie here so please be gentle!

Bit of a long story, I'm afraid, so please bear with me.

When I met my second wife, I'd recently been divorced and was paying for my daughter through the csa. She was aware of how my first wife had behaved and knew how much I had been hurt. Numerous affairs by the ex, withholding contact, and the constant struggle to run my present home while subsidising the ex and her string of "boyfriends" (I know I'm probably preaching to the choir). I started the merry go round of seeing a solicitor, arrangeing hearings, listening to her promise my solicitor/her solicitor/the judge that she'd be a good girl and give me access only for her to ignore the lot and still not let me see the kids. Every time it cost me a fortune and her nothing cos she got legal aid and I was working.

Move forward 15 years and the 2nd wife and I were going through a bad patch. She felt we were over stretched financially and she was having to work full time which she didn't like. I don't think she was messing about, I think we had just got into a horrendous rut, but she would've preferred to be a "lady of leisure". She asked for a separation and I agreed, though it was a further six months before she moved out. In that time she set herself up with a new fella, but there was no hard feelings. I may not have been in love with her but she was the mother of our two children and I wanted her to be happy.

She found herself somewhere to live fairly local and the kids went to live with her. She said she didn't want or need any money from me - she was still working full time and her new fella had a very well paid job. She also said I could see the kids any time I liked.

Then things began to go pear shaped. Shortly afterwards they moved again and I wasn't informed of their new address. None of her family would say where they were in case things got "nasty". I just couldn't face the access war again and she knew it.

Maybe 12 months later I got a phone call from the csa. Apparently she'd decided to stop working and sign on so they'd become involved. Now, I realise that access and maintenance are two separate issues, and I'm not proud of my response, but I told the person from the csa to F off and suggested that they'd not catch up with me before they were disbanded. Reckon they took that as a personal challenge.

Again, skip forward 12 months and an attachment of earnings letter arrived at my employer. I assume they'd got their figures from the inland revenue but they'd used the two highest weeks earnings I've ever had. Roughly double my normal wages. I rang them and talked about appealing and the chap from the csa said I could (but I'd have to pay in the meantime) or I could talk to my ex and come to some arrangement. I rang her and explained about how rediculous their figures were and she agreed to accept a lower figure which I paid by standing order straight to her. This went on for a couple of years until my son fell out with his mother and my step daughter explained to him that the tales of dastardly deeds performed by his father were just that, tales. At which point he got in touch and told me that my daughter was no longer in education but was working full time. I altered my standing order accordingly and started paying his maintenance directly to him until he too left education and started work.

Last month (some 4years since payments stopped) I received a letter from the csa saying I still owed my ex £20k.
This is made up of arrears from when they first contacted me till I stopped paying. I can have the amounts I paid offset against this if I produce bank statements in support @£5 per statement! Presumably I get to stand the cost of these?

At no point during the original set up, when I was discussing the unfair assessment with the csa or after setting up the arrangement with my ex, did anyone say that the original amount would stand like a millstone and come back to bite me later. If they had I would have appealed the amounts. Neither did anyone from the csa get in touch to say the amounts I was paying were not enough. Presumably, if either they or the ex were not happy, they would have been in touch before now?

My mother sadly died at the start of the year and left a small gift for my son but not my daughter. My daughter took her mother's side (dastardly tales brainwashing) and had no contact with her gradmother, even when she was very ill. I'm assuming this is all a result of her mother trying to "punish" me yet again, although the amount in my late mother's estate will barely cover the amount the csa are demanding.

Is there no way I can appeal this? I thought the whole thing was done and dusted 4 years ago. Would this be the final instalment or will they keep coming ad infinitum?

Thanks for taking the time and trouble to read this. If nothing else, it's been therapeutic to get it down on paper.